Anchoring - check it's ready

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Vyv Cox
Posts: 23
Joined: Tue Dec 16, 2008 10:35 am

Anchoring - check it's ready

Postby Vyv Cox » Sun Feb 01, 2009 3:06 pm

Firstly, there shouldn't be much twist in a properly laid anchor chain anyway. Secondly, under any kind of tension a swivel simply won't swivel anyway. And thirdly, it's a recognised weak point - especially with a sideways pull.


I'd like to make some comments on these statements.

Firstly, the twist. I agree that in general the worst that could happen between boat and anchor is a couple of changes of tide and/or wind direction, which will not normally be a problem. However, there is a far more significant source of twist. When a non-symmetrical anchor, which means just about anything other than a Fisherman, is hauled aboard with a modern, fast windlass, it spins quite significantly. In the murky waters of the UK this is not obvious (although the results can be) but in the Med it is seen very easily. The first problem that will occur is that the chain will twist. Some windlasses will allow the chain to rotate over the gypsy, with the result that it becomes increasingly twisted in the chain locker. Eventually the time will come when the chain cannot be lowered as it has jammed itself into a tight bundle. Other windlasses will not allow jumping the gypsy. Instead the chain will jam between gypsy and housing. A swivel does not completely overcome the problem but it helps a lot.

Secondly. It's not important that it swivels under load. It's when the anchor is being hauled, under relatively low load, that it does, going some way to preventing the first problem.

The third point is very misleading. I tested a large number of shackles and swivels for Yachting Monthly. The better swivels were about 1.5 times the strength of chain. Some were poor but I identified the design fault that caused this. The best shackles were almost as strong but the worst, mostly galvanised ones, were very poor, some less than half the strength of chain of the equivalent size.

The lateral loading issue is very simply dealt with and was the subject of another YM article. Inserting a couple of links of chain between the swivel and the anchor completely avoids the lateral loading but provides all the benefits of the swivel.

NormanS
Posts: 77
Joined: Mon Dec 22, 2008 4:49 pm

Re: Anchoring - check it's ready

Postby NormanS » Sun Feb 01, 2009 5:02 pm

Having anchored approximately three and a half thousand times, I think I can say I have some experience. I have never found twists in the chain to be a serious problem, and would certainly not advocate the use of a swivel.

In his article, Richard suggested using a shackle, one size up, for connecting the chain to the anchor, and this would seem very sensible. It is probably better to use a "Dee" shackle, rather than a "Bow" one for two reasons.
1. It is stronger.
2. There is less chance of it jamming between the cheeks of the bow roller.
(It is probably better to use the type of screw pin shackle where the pin is flush, for that reason).

Most of my anchoring has been with a 140lb CQR plough type anchor with five eighths (inch) chain, but I have now downsized my boat, and now use mostly a 20kg Bruce with 10mm chain.

I think that if a swivel was fitted, the only time it would operate would be the instant that the anchor came over the bow roller, when there is a brief moment when there is no tension on the chain. I can see no point in fitting a swivel for that.

Vyv Cox
Posts: 23
Joined: Tue Dec 16, 2008 10:35 am

Re: Anchoring - check it's ready

Postby Vyv Cox » Sun Feb 01, 2009 6:23 pm

I respect your experience, although I have probably anchored far more times than you have. However, that doesn't mean that you are right and I am wrong, or vice versa.

You don't say what other equipment you have but I assume with an anchor that big you have a windlass. Some models wind very slowly, in which case twist is unlikely to happen, I would think especially with a 140 lb anchor.

The cases I report were not made up, I have discussed the issue with many people and have heard numerous tales of windlass jamming. I have watched both my Delta and Rocna anchors rotating as I hauled them up. My own chain ties itself in knots after a month or so of anchoring, unless I unwind it periodically. Last year I saw an anchor twist violently when it emerged from the water, I assume when the accumulated twist unwound. It knocked a large chunk of gelcoat off the bow of the boat.

A 10mm Kong or Osculati swivel is stronger than any 10 mm shackle that I tested, except for the Wichard 17/4 PH one, which is what I use for all other anchor warp connections.

Phil
Posts: 193
Joined: Tue Dec 23, 2008 8:59 pm

Re: Anchoring - check it's ready

Postby Phil » Sun Feb 01, 2009 7:31 pm

Just a comment about shackles in general-rated ones-greenpin etc have a far better breaking strain than unrated of same size.Bow shackles can do all wonders of things-on my permanent mooring my swivel managed to thread itself thru the eye of a bow shackle and lock itself around the key-locking the swivel solid at 45 degrees out of line and ultimately untwisting my mooring warp.
I currently carry a spare 3/4 inch drop forged swivel which I would use if mooring to my anchor for any length of time.
I remain very unhappy about many of the smaller swivels whether stainless or galvanised as they often appear to be no more than a nut and bolt with a larger size nut threaded over the bolt and a couple of semicircular lengths of round section welded on to make the eyes.
Even the bigger ones I use with a 0ne ton rating I suspect are based on threaded lifting eyes matched up with eyes with a threaded pin.
Just take a careful look at your swivels and you will see what I mean.
Phil

NormanS
Posts: 77
Joined: Mon Dec 22, 2008 4:49 pm

Re: Anchoring - check it's ready

Postby NormanS » Sun Feb 01, 2009 8:32 pm

Re Vyv Cox.

Yes, one wouldn't want to handle a 140lb anchor and 5/8" chain without a windlass. Mine was hydraulic, and heaved in at the slow speed of 40 feet per minute, which probably gave ample opportunity for any twists to come out.

Quote: "I have watched both my Delta and Rocna anchors rotating as I hauled them up."

That suggests that your much vaunted swivel doesn't work.

Phil
Posts: 193
Joined: Tue Dec 23, 2008 8:59 pm

Re: Anchoring - check it's ready

Postby Phil » Sun Feb 01, 2009 9:29 pm

Norman-guess that was a small commercial boat of some sort-having said that and your comments about swivels strangely enough I bought some "preowned"one one quarter inch barred chain to cast into a concrete mooring block and it came complete with a one inch swivel-what a beastie!!
Phil

Vyv Cox
Posts: 23
Joined: Tue Dec 16, 2008 10:35 am

Re: Anchoring - check it's ready

Postby Vyv Cox » Mon Feb 02, 2009 8:52 am

Phil - Sorry, your comments on green pin shackles are just not true. They have a rated SWL but it is very conservative indeed. My destructive testing found that the rated shackles were amongst the weakest. In general the same size galvanised shackles were weaker than the stainless steel ones, some by a long way.

Actual loads delivered by wind and waves on an anchored boat is another subject though. I think (backed up by real measurements carried out by several authorities) it is highly unlikely that a chain in good condition would ever be overloaded enough to break it. Since the best shackles and swivels were stronger than the chain they can be assumed to be pretty safe.

NormanS - I said the anchors rotated. I didn't say the chain did!

Richard Thomas
Posts: 100
Joined: Tue Dec 16, 2008 7:33 pm

Re: Anchoring - check it's ready

Postby Richard Thomas » Mon Feb 02, 2009 5:21 pm

Vyv Cox wrote: I tested a large number of shackles and swivels for Yachting Monthly. The better swivels were about 1.5 times the strength of chain. Some were poor but I identified the design fault that caused this. The best shackles were almost as strong but the worst, mostly galvanised ones, were very poor, some less than half the strength of chain of the equivalent size.


I am grateful for Vyv's comments, particulary as they based both on experience and empirical tests, though not having read that particular issue of YM I would like to know what the design fault is, and whether it has also been recognised and corrected by manufacturers. Testing, and basing conclusions on empirical evidence, is very important, as is peer review by others. That's one of the great benefits of this kind of forum, and I've put a note in the original article pointing to Vyv's comments.

I suppose my own preferences show here: given a choice, I would eliminate any potential weak points. One way to eliminate the spin on an anchor is to rest it just before it breaks surface (conditions allowing), and it can untwist itself (should it need to) dampened by the water itself.

Experienced yachtsmen and women will make their own decisions about the make up of their ground tackle. I suppose my articles were aimed at the aspiring day skipper who maybe hasn't given a great deal of thought to the issues, and who may simply accept what is presented to him or her on the front of the yacht as being fit for purpose. Its not just swivels that cause problems: under-specifying the ground tackle on production yachts delivered with standard equipment is also, in my experience, a problem waiting to show itself.

A similar point might be made about the use of cable ties instead of paint - a point I make further down the same article. Having preferred the cable tie method for years, I sailed with a deep-sea compression diver (I think that's the correct title - he lived under water in a special atmosphere for days on end) who was responsible for safety checking other divers' work. It was his practice to cut away any cable ties he found on chain because of the risk of injury, and pointed this out to me. I still use cable ties, but am now more aware of the balance of risks.

Ed Wingfield
Posts: 34
Joined: Mon Dec 22, 2008 11:59 am

Re: Anchoring - check it's ready

Postby Ed Wingfield » Mon Feb 02, 2009 7:10 pm

I sailed with a deep-sea compression diver (I think that's the correct title

Might you mean saturation diver?

Richard Thomas
Posts: 100
Joined: Tue Dec 16, 2008 7:33 pm

Re: Anchoring - check it's ready

Postby Richard Thomas » Mon Feb 02, 2009 9:15 pm

Ed Wingfield wrote:Might you mean saturation diver?


Yes, that's exactly what I mean.


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